Kris at Low Tech Magazine explains how furniculars, those cable trains that were built up the sides of hills and mountains, often ran on water! The two cars wereconnected by cables, so you added 400 gallons of water to the one at the top, to make it heavy enough to roll down the hill while pulling up the lighter one at the bottom.

In Fribourg, Switzerland, they had a much better idea. One area in town is at the top of a hill, and the other at the bottom, separated by about 375 feet of elevation. And if there is one thing that is always flowing from the top to the bottom, it is sewage. Instead of running in a pipe, they pump some of it into the car at the top; at the bottom, they open it up and let it run into the lower sewer.